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From Michael Segel <mse...@segel.com>
Subject Re: "generated by default" question
Date Fri, 16 Jun 2006 05:25:00 GMT
On Friday 16 June 2006 12:10 am, Vic Ricker wrote:
> Daniel Noll wrote:
> > Ah.  I was making the assumption that the indexes were implemented
> > "properly."  For instance, an index should keep a certain amount in
> > memory in order to have a reasonable chance of running quickly.  So the
> > max and min should already be in-memory.
> >
> > I take it that Derby doesn't do this?
>
> The column doesn't necessarily have to have an index or even be unique.
>     An insert will only fail when there's a unique constraint on the
> column and the sequence generator returns a value that's already been
> used.
However, when you have an identity column, or even a unique constraint, you 
have what is considered a "backing index". That is an index created by Derby 
so that it could ensure uniqueness.

Again, this is irrelevant. You don't need to look at the index. You only need 
to know the CBV and the value that is being inserted in to the identity 
column. 

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